Dynamics of a dislocation bypassing an impenetrable precipitate: the Hirsch mechanism revisited

TL;DR

This study uses molecular dynamics simulations to analyze a dislocation bypass mechanism in copper, revealing a new process called the Hirsch mechanism that differs from the traditional Orowan process.

Contribution

It revisits the Hirsch mechanism, showing its critical stress is similar to Orowan's and emphasizing the role of shear stress in dislocation bypassing.

Findings

Hirsch mechanism involves dislocation leaving two prismatic loops.

Critical stress for Hirsch mechanism is comparable to Orowan stress.

Spatial shear stress inhomogeneity is crucial for the Hirsch mechanism.

Abstract

Dynamical process where an edge dislocation in fcc copper bypasses an impenetrable precipitate is investigated by means of molecular dynamics simulation. A mechanism which is quite different from the Orowan mechanism is observed, where a dislocation leaves two prismatic loops near a precipitate: i.e. the Hirsch mechanism. It is found that the critical stress for the Hirsch mechanism is almost the same with the Orowan stress, while the spatial inhomogeneity of the shear stress is essential to the Hirsch mechanism. We also find that the repetition of the Hirsch mechanism does not increase the critical stress.